For example, an evaporated fuel processing system 1 as shown in FIG. 8 is disclosed in Japanese Patent No. 5709573. The evaporated fuel processing system 1 has a float valve 3a and a cut valve 3b disposed on the upper portion of a fuel tank 2, and a control valve 6 and a high pressure two way valve 7 which are disposed on a vapor passage 5 for communicating between the fuel tank 2 and a canister 4.
Moreover, in FIG. 8, a reference numeral 3c shows a pump which sends the fuel inside the fuel tank 2 to an unillustrated internal combustion engine, a reference numeral 8 shows a pressure sensor detecting a pressure (tank internal pressure) inside the fuel tank 2, and reference numerals 9a, 9b show a filler pipe and a breather pipe which are provided between the fuel tank 2 and an unillustrated fuel lid, respectively.
The float valve 3a blocks an opening to the vapor passage 5 when the fuel pooled inside the fuel tank 2 is full, and prevents the fuel from entering the inside of the vapor passage 5. Moreover, the control valve 6 is configured with a normally-closed-typed solenoid valve in which a valve body biased by a biasing means such as a spring is seated on a valve seat. The control valve is in a closed state to shut off the flow of the evaporated fuel to the canister 4 side.
Furthermore, for example, the high pressure two way valve 7 is configured with the combination of a positive pressure valve and a negative pressure valve which are in a diaphragm type. The positive pressure valve opens when the pressure inside the fuel tank 2 reaches to a predetermined pressure, and the high pressured and evaporated fuel inside the fuel tank 2 is fed to the canister 4. The negative pressure valve opens when the pressure inside the fuel tank 2 is below a predetermined pressure. The evaporated fuel pooled in the canister 4 returns to the inside of the fuel tank 2.